The present invention relates to a cleaning blade for a latent image holding member used in an apparatus for forming an image using an electrophotographic process, such as a duplicator, a facsimile machine and a printer, and also relates to an apparatus for forming an image and a process for forming an image using the cleaning blade for a latent image holding member.
In an electrophotographic process, conventionally, the surface of a latent image holding member is charged and exposed to form an electrostatic latent image, which is then developed with a colored toner to form a toner image as a visible image, and the toner image is transferred to a transfer material, such as transfer paper, and fixed, for example, by a heat roll to form an image. Since a non-transfer toner generally remains on the surface of the latent image holding member after completing the transfer of the toner image, it is necessary that it is removed by a certain cleaning unit before conducting the next image formation step. Other foreign substances attached to the surface of the latent image holding member are generally removed along with the remaining toner by the cleaning unit.
As the cleaning unit for removing the remaining toner after transfer, various methods including a method using a fur brush or a magnetic brush and a method using a rubber blade are employed, and such a method is generally employed that the toner is scraped off by rubbing the latent image holding member with a cleaning blade formed with an elastic material because of the low cost and the high stability in performance. As the elastic material used as the material of the cleaning blade, polyurethane rubber is often used owing to the excellent wear resistance thereof.
In recent years, high image quality is demanded in the apparatus for forming an image of this kind, and the toner is demanded to have a smaller diameter and a spherical shape along with the demand for high image quality. The reproducibility of dots of a toner image formed on the latent image holding member can be improved by decreasing the toner diameter, and the developing property and the transferring property can be improved by using the toner of a spherical shape.
With respect to the production process of a toner, when the diameter of a toner is to be decreased by a pulverization method, which is one of the production processes of a toner that have been conventionally used, the yield upon production of the toner is deteriorated, and as a result, the cost of the toner is increased. Under the circumstances, in recent years, the polymerization method, in place of the conventional pulverization method, attracts attention as a production process of a toner having a small diameter and a spherical shape because it is advantageous in cost even when the toner having a small diameter and a spherical shape is produced. The polymerization method includes a suspension polymerization method, an emulsion polymerization method and a dispersion polymerization method.
However, in the case where the toner having a small diameter and a spherical shape (hereinafter, sometimes referred to as a xe2x80x9cspherical tonerxe2x80x9d) is used, there are some cases where good cleaning performance cannot be obtained by the blade cleaning method particularly using a rubber blade. In particular, the cleaning property is remarkably deteriorated in the case of a toner of a substantially spherical shape having a shape factor SF of the toner of 125 or less. Even in the case of a toner having a shape factor SF of from 125 to 135, a toner having a substantially spherical shape is contained when the toner has a shape distribution, and there is a tendency that the cleaning property is deteriorated with the lapse of time.
The cleaning property tends to be deteriorated when the toner used for development has a smaller diameter and a sharper particle size distribution. Particularly, the deterioration of the cleaning property becomes conspicuous under a low temperature and low humidity environment. Although the cleaning property under a low temperature and low humidity environment can be improved by increasing the contact pressure of the cleaning blade to the latent image holding member, when they are used under a high temperature and high humidity environment with the high contact pressure maintained, the adhesion strength of the latent image holding member and the cleaning blade is increased to increase the deformation amount of the tip of the blade, whereby breakage of the blade edge or curling of the cleaning blade sometimes occurs. In order to obtain good cleaning pry under any environment with long term use when the spherical toner is used, it is necessary that the rubber property and the set conditions of application of the cleaning blade are strictly adjusted, and it is extremely difficult to retain the balance thereof.
Because a latent image holding member is rubbed with a rubber blade to scrape off a toner in the cleaning method using a rubber blade, the tip of the edge of the rubber blade is deformed by the friction resistance to form minute cuneate spaces between them. The toner having a smaller diameter is liable to invade into the spaces to the tip of the edge, and the toner invading to the tip of the edge is difficult to be replaced to form a remaining region. No cleaning failure occurs under the conditions where the friction coefficient between the toner in the remaining region and the latent image holding member is relatively small, and the toner slides on the latent image holding member. However, when the friction coefficient between the toner and the latent image holding member is increased by drop off of an external additive due to friction with the latent image holding member, the rolling resistance of the spherical toner is smaller than the conventional pulverized toner of an irregular shape, and it is considered that the spherical toner starts to roll between the cleaning blade and the latent image holding member to go through them.
In the case of a spherical toner having a further sharp particle size distribution, because it is liable to suffer the closest packing in comparison to the toner of an irregular shape, it is considered that consolidation is liable to occur in the minute spaces in the vicinity of the contact point between the edge of the cleaning blade and the latent image holding member to increase the friction force between the latent image holding member and the toner, whereby the toner is liable to roll. Because the charged amount of the toner becomes high under a low temperature and low humidity environment, the adhesion force between the latent image holding member and the toner is increased to accelerate the rolling of the toner.
In order to prevent the cleaning failure of the cleaning blade in an apparatus for forming an image using the spherical toner, a process for forming an image using a mixture of a spherical toner and a toner of an irregular shape is proposed in JP-A 131547 and JP-A6-148941. In these processes, however, since a mixture of a spherical toner and a toner of an irregular shape is used as a toner for development, a problem occurs in that a precise and uniform image and a high transfer efficiency, which is an advantage of the spherical toner, cannot be obtained in comparison to the case using only the spherical toner.
JP-A-8-254873 proposes that in an apparatus for forming an image constituted by plural developing units for developing images of different colors, a toner of an irregular shape is installed in at least one of the developing units, and a spherical toner is installed in the other developing units. The process also has a problem in that a precise and uniform image and a high transfer efficiency, which is an advantage of the spherical toner, cannot be obtained in comparison to the case where development is conducted by using only developing units having the spherical toner installed. Furthermore, the advantages cannot be obtained in an apparatus for forming a full color image by a tandem type.
A method of supplying a lubricating agent to a latent image holding member to prevent clog failure of a cleaning blade in an apparatus for forming an image using the spherical toner (for example, JP-A-5-188643) is propose. However, cleaning failure occurs when the supply of a lubricating agent to the latent image holding member becomes shore and adverse influence due to filming on the latent image holding member occurs when the supply is excessive. Therefore, it is necessary that the lubricating agent is uniformly supplied to the latent image holding member for a long period of time, and thus the designing of the apparatus involves terrific difficulty. Furthermore, since the apparatus is recently downsized, it is very difficult to assure a space for arranging a unit for supplying a lubricating agent that supplies a lubricating agent directly to the surface of the latent image holding member particularly in an apparatus for forming an image using a latent image holding member of a small diameter. In particular, it is necessary to provide the unit for supplying a lubricating agent on each of the latent image holding members in an apparatus for forming an image of the tandem type, and it is considerably disadvantageous in cost reduction.
The invention has been made in view of the foregoing circumstances and provides, at a low cost, a cleaning blade for a latent image holding member that ensures good cleaning property of the latent image holding member irrespective to a temperature environment upon using without deterioration in image quality even in an apparatus for forming an image using a spherical toner, as well as an apparatus for forming an image and a process for forming an image.
The inventors have conducted earnest investigations to attain the aims of the invention, and as a result, it has been found that the aims can be attained by using a cleaning blade having particular properties to accomplish the invention.
According to an aspect of the invention, the cleaning blade removes a remaining toner by contact with a latent image holding member under pressure, the cleaning blade containing an elastic material having a 300% modulus of about from 14,700 to 29,400 kPa (about from 150 to 300 kg/cm2) and a tearing strength of about 68,600 N/m or more (about 70 kgf/cm or more).
According to another aspect of the invention, the apparatus for forming an image contains a latent image holding member, a latent image forming unit for forming a latent image on a surface of the latent image holding member, a developing unit for developing the latent image formed on the surface of the latent image holding member with a toner to form a toner image; a transferring unit for transferring the toner image formed on the surface of the latent image holding member to a transfer material; and a cleaning unit for removing a remaining toner on the surface of the latent image holding member after the transfer. The cleaning unit has a cleaning blade rubbing the surface of the latent image holding member therewith, and the cleaning blade has an elastic material having a 300% modulus of about from 14,700 to 29,400 kPa (about from 150 to 300 kgf/cm2) and a tearing strength of about 68,600 N/m or more (about 70 kgf/cm or more).
According to a further aspect of the invention, the process for forming an image contains a latent image forming step of forming a latent image on a surface of a latent image holding member, a developing step of developing the latent image formed on the surface of the latent image holding member with a toner to form a toner image; a transferring step of transferring the toner image formed on the surface of the latent image holding member to a transfer material; and a cleaning step of removing a remaining toner on the surface of the latent image holding member after transfer. The cleaning step contains a step of rubbing the surface of the latent image holding member with a cleaning blade, and the cleaning blade contains an elastic material having a 300% modulus of about from 14,700 to 29,400 kPa (about from 150 to 300 kgf/cm2) and a tearing strength of about 68,600 N/m or more (about 70 kgf/cm or more).
As described in the foregoing, the reason why the cleaning property of the spherical toner is poor as compared to the toner of an irregular shape is ascribed to the face that the spherical toner having a low rolling friction coefficient rolls between the cleaning blade and the latent image holding member, and in order to improve the cleaning property of the spherical toner, it is important how to stably suppress the rolling of the spherical toner for a long period of time irrespective to the environment of use.
The inventors have found that the use of a cleaning blade containing an elastic material satisfying a 300% modulus of about from 14,700 to 29,400 kPa (about from 150 to 300 kgf/cm2) and a tearing strength of about 68,600 N/m or more (about 70 kgf/cm or more) is effective to stably suppress the rolling of the spherical toner at a minute deformed part at the tip of the cleaning blade for a long period of time, so as to accomplish the invention.